1. Field of the Invention
The invention relates to a semiconductor device having metal gate and manufacturing method thereof, and more particularly, to a semiconductor device having metal gate and manufacturing method thereof integrated with the gate last process.
2. Description of the Prior Art
Polysilicon is conventionally used as the gate electrode in a semiconductor device, such as the metal-oxide-semiconductor (MOS) transistor. However, with a trend toward scaling down the size of the semiconductor device, the conventional polysilicon gate has faced problems such as inferior performance due to boron penetration and unavoidable depletion effect which increases equivalent thickness of the gate dielectric layer, reduces gate capacitance, and worsens a driving force of the devices. Therefore, work function metals are used to replace the conventional polysilicon gate to be the control electrode that competent to the high dielectric constant (high-K) gate dielectric layer.
The conventional dual metal gate methods are categorized into the gate first process and the gate last process. In a conventional dual metal gate method applied with the gate first process, the anneal process for forming the source/drain ultra-shallow junction, and the silicide process are performed after forming the metal gate. The thermal budgets always make the gate first process face challenges for material choices. Consequently, the gate last process is developed to provide more material choices for the high-K gate dielectric layer and the metal gate, and thus replaces the gate first process.
Though the gate last process is able to avoid processes of high thermal budget and to provide more material choices for the high-K gate dielectric layer and the metal gate, the gate last process still faces integration requirements, such as to ensure the metal gate obtains the expected height, for the complicated processes.